Printed circuit boards (PCBs) embedding parallel conductive wires therein are widely used throughout the electronics industry particularly in applications for interconnecting electronic modules on which electronic components are mounted in high density. Ribbon cables are also widely used to connect PCBs to each other and to other equipment. In U.S. Pat. No. 4,660,125 issued to Purdy et al on Apr. 21, 1987, ribbon cables provide interconnection of a cabinet and a slidable drawer in which the PCB circuit cards of electronic components are mounted. A standard ribbon cable assembly, however, has no electric or magnetic shielding.
To provide electric and magnetic shields, flexible printed circuit boards in which parallel conductive wires are sandwiched between a mesh, have been proposed. In telecommunication applications, these conductive wires include pairs of tip and ring conductive wires for telephone lines. The conductive wires interconnect components to transmit electric signals between components. In known flexible printed circuit boards, the conductors forming the mesh generally intersect each other at right angles, and the longitudinal axes of the tip and ring conductive wires are oriented to run parallel to the intersections of the mesh. In such an arrangement, it is difficult to control placement of the parallel conductive wires relative to the intersections of the mesh. As a result, one conductive wire may be closer to the intersections of the conductors of the mesh than the other conductive wire. Should this happen, the capacitance between that one conductive wire and the mesh will be less than the capacitance between the other conductive wire and the mesh. Due to this unbalance, higher levels of cross talk are unavoidable, particularly between adjacent pairs of conductive wires transmitting signals. At audio frequencies, this was not a serious problem. However, at the very high frequencies and bit rates now being transmitted, this unbalance has become a critical problem.